GOOD news: the older you get, the better the sex. Bad news: it only applies if you're an azure damselfly.

Far from being demure, these striking, iridescent creatures with delicate wings are the sex bombs of the animal kingdom. The bodies of the copulating males and females even form a romantic image in the shape of a heart.

And their bouts of love-making can last two hours. After an initial 30 minutes of rampant sex, pairs remain conjoined for a further 90 minutes while females looks for a place to lay their eggs.

For the damselflies, it doesn't matter how much sex they have had in the past, they can still keep on going until they die

Dr Christopher Hassall, of Leeds University School of Biology

The secret life of the azure damselfly has been laid bare by researchers who discovered how these close relatives of dragonflies never lose their libido nor show signs of tiring from frantic sexual activity.

Scientists tagged more than 1,000 azure damselflies in a pond in Hampshire and spent two years observing them.

Dr Christopher Hassall, Marie Curie Fellow in the University of Leeds' School of Biology, led on the analysis of data. He said: "For the damselflies, it doesn't matter how much sex they have had in the past, they can still keep on going until they die and they don't appear to pay a price for it.

"It was Aristotle who first proposed that too much sex might shorten your lifespan. That was over 2,000 years ago, but that doesn't seem to bother the damselflies."

Details of the study are being published in the Journal of Animal Ecology and are based on field studies led by Professor David Thompson of the University of Liverpool. It also involved researchers from Leeds, Carleton University in Canada and the University of Oulu in Finland.

By lifting the lid on the insects' sex life, scientists hope to make important medical and environmental discoveries.

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The damselflies even form a distinctive heart-shape when mating

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Dr Hassall added: "It is an excellent model species, but the findings are likely to provide insights not just for damselflies and dragonflies but for other groups of insects of greater public health interest: mosquitoes and tsetse flies, for instance. "In order to understand insect populations in the wild, we need to know how reproduction works across a lifecycle and this study has changed how we look at ageing and reproduction in these insects."

One thing to bear in mind is that old age is relative - most of the damselflies die within a week of arriving at the pond.